Automatic telephone-exchange system



Oct. 20,192 1,551,991

I A. H. DYSON AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed March 24, 1906 ZSheets-Sheet 1 Oct. 20, 1925- 155K991.

A. H. DYVSON AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed March 24, 1906 2 sheets-snwt'z once with my invention. In

Patented Oct. 20, 1925.

UNITED STATES PATENT orrics.

sum 1:. DYSON, or cmcaco, rumors, assumes, a: mu Assmnmraro KEL'LOGG SWITCHBOABD & SUPPLY COMPANY, A CORPORATION Oil ILLINOIS.

AUTOMATIC TELEPHONE-EXCHANGE SYB'I'.

Application and mm; a, 1m. mmm). son.

To all whom it. may cmwern:

Be it'known that I, ALFRED H. DYSON, a resident of Chicago, county of Cook. and State of Illinois,- have invented new and use ful Improvements in Automatic Tele hone- Exchange Systems, of which thev fol owing is a specification.

My invention relates to automatic telephone exchange systems in which'seleetor switches are employed to select the groups of lines in which the lines of thii wanted subscribers are included, and in which connector switches are emplo ed, which connect directly with the wanted ines.

My invention is especially directed to the improvement of the circuits employed for operating the connectors and of the means employed in connection with them for including ringing current in circuit with the called subscriber's line to signal the substation, and for releas'in the switches employed. in a connection at the conclusion of the conversation. I

Referring to-the drawings, in Fig. 1 I show a subscribers station connected by a line with a selector circuit at the exchan e and a connector circuit arran ed in accor a second substation connected by its line with a selector, and the circuit of a connector embodying my invention in a form varying from that shown in Fig. 1.

My invention is directed to circuit arrangements only, and I have therefore not shown any particular switch mechanism to be operated by the circuits as any desired or known mechanical arrangement may be employed, for instance such a switch mechanism as that shown in United States Letters Patent to A. H. Dyson, No. 830,981 dated September .11, 1906.

The substation at A includes the usual condenser and call bell normally. held in bridge of the line limbs P and S by the hook-lever 6, while the transmitter is adapted, upon the removal of the receiver from the hook lever, to be connected across the two line limbs by the closure of contact 6-7, the receiver being in local circuit with the secondary winding of the induction coil. The arrangement at the substation A also includes the dial 1, which is provided with i 2 I show ratchet teeth of insulating material and which 18 adaptedjor rotation by hand in the direction indicated by the arrow, the said dial being returned in the opposite direction when rotated and released by the spr ng fastened to it. When so operated, its teeth cause the spring 2 to engage its associated contact spring and to connect ground G with limb P of the line as many times as teeth are passed below the spring. titer the last movement of spring 2, the dial in its return causes spring 3 to en age its associated sprm a single time and t ion disengage it, where y ground G is momentar- 11y connected to limb S of the line. Springs 4 and 5 are provided in the transmitter circuit and are normally held'in contact by a sto upon the dial 1. When the dial is in ct er than normal position, however, the movement of the sto removes the tension from spring 4. which isengages 5 and there. by maintains 0 en the circuit through the transmitter whi e the dial is being operated and the switching im ulses transmitted.

A key 9 is provide for openin the metallic circuitof the line extending t rough the transmitter for ringing purposes.

The hook-lever 6 with arm 8, is so arranged that when the receiver is removed arm 8 passes to the left over the extremity of spring 12 to a position such that when the receiver is replaced, its movement to the right will cause the springs 12, 11 and 10 to be for a moment simultaneously connected, whereby the two line limbs are at the same time grounded.

The selectorv shown in Fig. 1 includes the terminal contacts 14, 15 and 16, multipled to a plurality of connector switches in the usual manner and employed when another subscriber is seeking connection with the line of subscriber A. Contacts 15 and 16 are connected to limbs P and S respectively, while contact 14 is connected through ofinormal switch spring 13 and its normal contact and the winding of cut-off relay 21 to battery 66.

Connected to limb P through side switch arm 19 and its normal contact 'is primary relay 22 whose circuit. extends through an armature of relay 21 to battery, the said relay 22 closing when actuated, the circuit of primary magnet 27 employed to move wipers 29, 30 and 31 to select the group of connector switches common for connection to the 100 line group of subscribers, among which the line of the wanted subscriber will be included.

The secondary relay 23 is connected to limb S of the line through side switch arm and to battery 66, and by its armature controls the circuit of private magnet 28, which has the function when energized and de-energized of moving side switch arms 17, 18, 19 and 20 one step in a downward direction from their positions as shown to engage respectively their second contact points. S1de switch arm 17 when brought to engage its second contact, closes circuit through secondary magnet 24, which vibrates its armature to move the switch wipers 29, 30 and 31 in search of idle connector switch terminals of the selected grou and the enga ement of 17 with its thir contact opens t e circuit of 24 which brings the wipers to rest. Side switch arm 18 when brought to engage its second contact, connects the rivate wiper 29 throu h the winding of re ease relay 25 with the winding ofprivate magnet 28 to renderthe said private magnet sensitive to the grounded or ungrounded condition of contacts 32 of the connector switches of the group, so that the said magnet 28 will release its armature as soon as 29 reaches an idle or ungrounded contact, which causes the side switch arms to move to their third positions. The windings of rela 25 andmagnet 28 are so proportioned t at a flow of current through 25 in series with 28 is not sufiicient to cause the attraction of its armature, although the armature at 28 will be attracted. Side switch arm 18 when in its third position, connects ground G to wiper 29 and the contact 32 of a selected idle connector to render the said connector busy, and also places release relay 25 in operative relation with contact 32 of the connector in order that at the proper time it may be energized by a flow of current initiated at the connector to cause the operation of the release magnet 26 whereby the selector is caused to return to normal;

Wipers 29, 30 and 31 are fastened to shaft I a, WhlCll shaft, with the form of switch before referred to, is given a series of upward steps to select the group of switches wanted, under the influence of primary magnet 27, while under the influence of secondary magnet 24 the shaft receives arotary step or ste s, carrying with it the switch wipers an moving them over successive terminal contacts 32, 33, 34 of connectors, which contact, as indicated, are multipled to other first selectors.

The connector shown at D includes the primary relay 41, connected to contact 33 through arm 36 and the battery 66, controlling by the spring 48 and its alternate contact the operation of primary magnet 42 when arm 35 is in its normal position, and the operation of secondary magnet 45 when arm 35 is in engagement with its second contact.

The secondary relay 43, connected to contact 34 through side switch arm 37 and to battery 66, controls by its armature s ring 46 the private magnet 44, the latter eing arranged. when energized and de-energized to move side switch arms 35, 36, 37, 38, 39 and 40 downwardly to engage the contacts of their respective sets adjacent to those engaged by them prior to its energization and de-energization. Side switch arm 35 in its normal position connects magnet 42 with spring 48;, in its second position connects magnet 45 with said spring, and in its third position connects ground G through the armatures of relays 41, 50 and 51 with ringing-relay 58 and battery so that when all of the ,saidrelays are 7 e-energized, 58 will be energized and will include the ringin generator 59 in circuit with wi ers 64 an to cause the bell of the cello subscriber to ring. Arms 36 and 37 in their normal and second positions connect the windings of 41 and 43 with contacts 33 and 34 and in their third positions complete the talking circuit of the connector, (and leave 0 en the circuits of relays 41 and 43) the talkmg circuit being indicated by the heavily marked lines. Arm 38 in its second position connects wiper 63 with a switch contact of private magnet 44, which contact is closed when the magnet is operated so that should wiper 63 be brought to rest in contact with the terminal of a busy line, release magnet 62 may thereupon be operated by current from the grounded terminal of the busy line through the closed switch contact of magnet 44 to battery 66. When in its third position side switch arm 38 connects ground G" to wiper 63 and the.

terminal of the called line engaged by it and to the multiples of the said terminal rendering the called line busy with respect to other connectors having access to it. Arms 39 and 40. when engaging their first and second contacts are in open circuit, and when engaging their third contacts complete the talking circuit to wipers 64 and 65 respectively. Relays 50 and 51 permanently connected from the opposite sides of battery 66 to the two talking conductors of the connector, are by the operation of switch arms 36 and 37 brought under the control of the calling subscriber A in such manner that by the operation of key 9 the subscriber is able to interrupt the flow of current through both of them and cause retraction of their armatures 53 and 55 to complete a circuit from ground G through arm 35,

spring 48, armatures 53 and 55 and the windin of ringing rela 58 to battexly to cause t e energization o relay 58; an by the operation of the hook lever the subscriber at A can cause the de-energization of relay 50 by .shuntin current out of its windin by the grounding of limb P of the line, w ile current continues through rela 51 to ground at the substation over limb this being the condition wherein the armature 52 is retracted and armature 54 is attracted to complete circuit through the devices for releasing the switches. 4

Relays 56 and 57 are connected from the opposite sides of battery 66 by means of side switch arms 39 and 40, when in their third positions, to wipe-rs 64 and 65 and the limbs of the called line and through their windin 's is passed the current for energizing the called subscribers transmitter.

At the conclusion of the conversation and the replacing of the receivers upon the hook levers, current is shunted from relay 56, while current continuing through relay 57, its armature is attracted to close circuit through release magnet 62 and subsequently open circuit therethrough to'relea'se the connector. Assuming an exchange of 1000 subscribers, the usual and preferred arrangement of apparatus will be as follows. Each subscribers line will be provided with a selector, whose wipers will be capable of being caused to reach terminals of '100 connectors. For an exchange of this size, 100 connectors would be required and each connector would be arranged so that its wipers could select multiple terminals of 100 subscribers lines of the 1000. The 100 connectors would therefore be divided into groups of ten, one such roup being assigned for connection to eac li 100 lines. The terminals of each roup of connectors would be grouped betore the Wipers of each selector in separate levels (when switches of the character before mentioned are employed), upward steps of the wipers selecting the several groups, and rotary steps selecting an idle switch of the proper group. 7

Each group of 100 subscribers lines have their terminals multipled to 10 connectors, the terminals being divided into groups according to the tens of the 100, each group being placed on a different level of a connector, upward step-by-step movements of the connector wipers being caused to select the tens group of the 100, and rotary movements or the wipers being caused to select the particular line wanted of the tens group.

' The calling subscriber first operates his selector to pick the group of connectors of the hundred lines including the linewanted. The selector then automatically picks out an indifi'erent .idleconnector and laces it under control of the subscriber, wio then transmits impulses to the connector to seto select the particular line wanted out of the tens roup..

Assuming that subscriber A desires to have conversation with subscriber No. 34.5,

subscriber A first removes his receiver and turns to the proper extent the dial 1 and releases it, whose teeth operate upon springs 2 and 3, sending three 1m ulses of current over limb P of theline, an thereafter asingle im ulse over limb S of the line. The three impulses flowing from round G throughspring 2, key 9, limb T, arm 10, relay 22 to battery, energlze and de-energlze the said relay three times, a corresponding number of impulses flowing from ground G, armature spring of relay 22, armature of magnet 28 t rough primar magnet 27, the resulting energizations ant de-energizations of 27 causing wipers 29, 30 and 31 to select a group of connector terminals belonging to connectors each of which is common for connection to the third 100 line group of subscribers including Nos. 300 to 399. With the first movement of the selector off-normal switch spring 13 engages its alternate con tact to connect ground G with connector contact 14, to render the, line of A busy to incoming calls via the connectors.

The single impulse of current before referred to flows from ground G, through spring 3, over limb S, through si-de switch arm 20, relay 23 to battery, the resulting ener 'ization of relay 23 causin a single impifise to flow from ground through the armature springs of said relay and private magnet 28 to battery, causin the energization and de-energization of said magnet, whose armature upon its retraction moves the side switch arms 17, 18, 19 and 20 to engage their res active .second contacts. Arms 19 and 20 w ien so moved leave unaltered the connections of relays 22 and 23 to limbs S and P respectively. Arm 17 in its new position closes circuit from ground through secondary magnet 24-. to battery, causing the magnet to attract and release itsarmature, its circuit being of vibratory char-v acter. This energization and de-energization of 24: moves wipers 29, 30 and 31 to ongage terminals of the first connector oi the selected group. In accordance with the well known practice, a mechanical connection exists between the armature of magnet 24 and the side switch arms, of such character that (unless private magnet 28 is energized) upon the attraction and release of the armature of 24, the side switch arms will be moved to their third position. Assuming first that contacts 32, 33 and 34 belong to a connector which is in its normal or idle condition, upon the engagement of wiper 29 with contact 32 no flow of current results through private magnet 28 which is now 1 connected with contact 32 by arm 18 and wiper 29, because as shown, the said contact 32 is on open circuit. Side switch arms 17, 18, 19 and 20 therefore move to their third positions, the movements of arms 19 and 20 cutting off relays 22 and 23 and completing the talking circuit of the selector (indicated by heavy conductors) while arm 17 opens the circuit of secondary magnet 24 to prevent further operation thereof. The arm 18 connects ground G through the winding of release relay 25 and wiper 29 to contact 32 and its multiples, rendering the connector busy to theother selectors having access to the multiple terminals of it.

Assuming now that at. the time when wiper 29 engaged contact 32, as before described, another selector was connected to a multiple of 32; upon the closure of contact 2932 21 flow of current would result from ground G at the other selector through its arm 18, its relay 25, its wiper 29, to multiple of 32, thence through contact 32, 29 of Fig. 1, relay 25, arm 18 its second contact, private magnet 28 and to battery, which flow would energize magnet 28, Whose attracted armature as before mentioned would prevent movement of the side switch arms of the selector, so that a second energization of secondary magnet 24 would resu t, bringing wipers 29, 30 and 31 to engage contacts, terminals of the second connector of the selected group. The windings of relays 25 and of magnet 28 are so proportions that when current passes in series through the said windings to cause 28 to attract its armature, relays 25 do not receive suilicient current to cause their armatures to be attracted.

Should the second connector be in use, a path forcurrent similar to that above described, will exist as soon as wiper 29 engages the contact of the second connector. and the side switch arms will hence remain immovable. Secondary magnet 24 will therefore continue its energizations and deenergizations seeking terminals of an idle connector until such terminals are found, when the ensuing de-energization of private magnet 28 will allow the side switch arms to pass to their third positions, with results as before described.

An idle connector having been selected, subscriber A by dial 1 now sends four impulses of current over limb P of the line from ground G, the current passing through side switch arm 19, contact 3033, arm 36, relay 41, to battery, causing four energizations and dc-energizations of said relay, whose attracted and released armature causes four impulses to flow from ground G through spring 48, armature of magnet 44', arm 35, primary magnet 42 to batter Wi ers 63, 64 and have before them mu tip e terminals of the lines of subscribers 300 to 399 arranged in groups of 10 and,

the four energizations of primary magnet 42, now occurring, cause wipers 63, 64 and '65 to select a tens roup of terminals of subscribers lines so disposed that the fifth terminals of the group are those of the line 23-15.

A single impulse of current flowing from ground G over'limb S, succeeding the said four impulses over limb P, passes through side switch arm 20, contact 31-,34, arm'37, relay 43 to battery, causing 43 to attract and release its armature and an impulse to flow from ground G through spring 46, its associated contact spring, private magnet 44 to battery. The said magnet 44 attracts and releases its armature, and upon the release thereof side switch arms 35, 36, 37, 38, 39 and 40 move to engage their respective second contacts.

Subscriber A by dial 1 now sends 5 impulses from ground G through spring 2 over limb P and over the before traced path through relay 41, whose five times attracted and'releascd armature causes five impulses to flow from ground (.i through spring 48, armature of magnet 44, arm 35, its second contact and secondary magnet 45 to battery, which magnet 45 affects five secondary or rotary switching movementsof wipers 63, 64 and 65, bringing them to engage the fifth contacts of the selected tens group, which as before stated, are multiple terminals of the subscribers line No. 345.

The circuit of such a line is shown at E in Fig. 2 (which circuit is identical with the circuit C of Fig. 1) and for the better understanding of the operation of the connector of Fig. 1 with res eat to the called line, the said Fig. 2 may e placed so that wipers 63, 64 and 65 of Fig. 1 are approached to terminals 14, 15 and 16 of the line of subscriber B which mabe considered as that of the called su scriber No. 345.

A single impulse flowing from ground G,

succeeding the last of the five impulses over limb P, fiowsthrough spring 3, over limb S, contact 3134, arm 37, relay 43 to battery, which relay, attracting and releasing its armature causes a second energization and de-energization of private magnet 44. As soon as the said magnet attracts its right hand armature,a connection is completed from the active side of battery 66, through winding of release magnet 62, armature of relay 44, its second contact and arm 38, to wiper 63 and terminal 14 of the called line. As will be observed this terminal is normally connected to the active side of battery and in this condition no energization of release magnet 62 is possible, and upon the de-energization of private magnet 44, side switch arms 35, 36, 37, 38, 39and 40 leave their second contacts and engage their third contacts. In so doing, arms36, 37, 39 and lit) necto'r', arms 36 and 37 in addition cutting ofithe winding of relays 41 and 43 from contacts 33' and 34. Arm 38 connects ground (it through contact 63--14 and cutofi relay21 of Fi 2, of the called line with v the active side battery. 66 and the cut-off relay is operated to 0 en the normal battery connections to limbs l and S oi the called line. The connectin of ground G: to contact 14 and its mu tiples also renders the called line busy to others connectors, as will be hereafter explained. The movement of arm 35, Fig. 1 connects ground G through armature of relay 44, spring 48 and its normal contact to armature 53and would complete circuit through armature 55 and ringmg relay 58 were it not for the fact that at this time relays 50 and 51 are both energized by current flowing from ground throng 1 relay 50, through its third contact and arm 36, contact 33-30, arm 19, limb P, key 9, contact 6-7, (the receiver being removed) through the transmitter supplying current to energize it, through contact 5-4, returning over limb S, through arm 20, contact 31-34, arm 37 and its third contact, re1ay 51 to battery 66. Y

Subscriber A now depresses key 9 to open circuit through the substation causing relays 50 and 51 to be simultaneously deenergized, and their retracted armatures 53 and 55 com lete the-before mentioned circuitthroug ringing'relay 58, whose attracted armatures include generator 59 in circuit with the called line to rin the substation bell. When subscriber releases key 9, again closing circuit through-the substation, relays 50 and 51 attract armatures 53 and 55 to open circuit through relay 58, whose thereupon retracted armatures disconnect the generator from the called line.

When subscriber B removes his receiver, contact 6-7 (Fig. 2) is closed and circuit is completed from ground through relay 56, arm 39, its third contact, contact 64--15, over limb P, through the transmitter of the substation, energizing it for talking, returning over limb S, contact 16-65, arm 40 and relay 57 to battery, said relays 56 and 57 attracting their armatures. The two subscribers are now in conversation through the two condensers placed in opposite sides of the talking circuit at the connector.

Assumin that at the end of conversation, subscriber B replaces his receiver before subscriber A, the resulting momentary and simultaneous grounding of limbs P and S of his line by springs 10, 11 and 12, shunts current from the winding of relay 56, whose armature is retracted, while current continues through relay 57. Circuit is thereby momentarily closed from ground, through the back contact of relay 56 and armature of relay 57, and through release magnet 62 to battery, the resulting energization and de-energ'ization of release magnet 62 cans- .lllg

the return of the connector to normal. The release of the selector remains to be accomplished from substation A and occurs in the following manner. The side switch "arms of the connector having returned to normal, the simultaneous grounding of limbs P and S of the line of subscriber A, when he replaces his receiver, causes simultaneous impulses of current to flow through relays 41 and 43 and their simultaneously attracted armatures complete circuit from ground G at the selector, through its third contact and arm 18, release relay 25, contact 29, 32, through spring 49 and its associated contact, its associated contact and spring 47, release magnet 62 to battery 66. Relay 25 is thereby energized and effects the energization of release magnet 26 by a flow of current passin from ground G through said magnet an the attracted armature of 25. As soon as arm 8 of hook lever 6 at substation A passes over the end of spring 12, ground is removed from the line limbs, relays 43 and 41 are de-energized, and circuit. o ened through relay 25 whose retracte armature opens the circuit of release magnet 26 and upon the de-energization of 26 the selector is restored.

Assuming that subscriber A replaces his receiver in advance of B, the resulting grounding of the two line limbs takes current from relay 50, whose armature 52 is retracted, while current continues through relay 51, whose armature 54, continuin in its attracted dposition, allows current to ow from groun G at the selector, through side switch arm 18, release relay 25, contact 2932, through armature 52, its back contact and armature 54, release magnet 62 to battery 66. The resulting attraction of the armature of relay 25 causes the energization of release magnet 26 of the selector. As soon as, with the return of the hook lever, ground is removed from the line limbs as substation A, circuit is broken through both (relays 50 and 51, release magnet 62 is de-energized, restoring the connector and release relay 25 efiects the deener ization of release magnet 26 restoring the rst selector.

Returning now to the oint at which wipers 63, 64 and 65 were rst brought to engage contacts 14, 15 and 16 of the called line, if the said line were already in use its terminal 14 would be connected to ground G, at its own selector, or to ground G, at a connector, depending upon whether the line or B was a calling or 9. called line. In such case the impulse of current energizing relay 44, occurring immediately after the establishment of contact 63-14, would, by the attraction of the right hand armature of relay 44, complete a circuit from ground at contact 14 through wiper 63, arm 38, and its second contact, armature of relay 44, release magnet 62 to battery 66. Release me at 62 would be energized until the impu e through 44 ceased when the retracted armature of 44 would efi'ect the de-energization of release magnet 62 and the return of the connector to normal. As soon as the connector is restored, oif normal switch 61 engages its associated contact and busy machine 60 is thereby brought into circuit with the line of subscriber A through arm 36 and its normal contact, and the subscriber A receives in his telephone the busy signal.- He thereupon replaces his receiver,

and the return to normal of the selector follows the momentary simultaneous energization of rela s 41 and 43 in the manner before describe The circuit shown in Fin. 2 includes the substation B and the first selector F (similar respectively to the substation A and selector C of Fig. 1) and the connector F difi'eriug from that shown at D in Fig. 1 in this respect: that a differential relay 67 is provided through whose winding 71 is supplied the current for rela s 51 and 57,whilc through its winding 0 is supplied current for energizing relays 50 and 56. Its armatures 68 and 69 are arranged when the core of the relay 67 is magnetized to open the circuits of relays 50 and 56 respectively; in

order to insure the de-energization of these relays when the subscribers at the respective substations replace their receivers. The structure employing the relay 67 would be desirable in exchanges where a material difference of ground potential existed between the exchange and the outl ing substations. Should there be such a di erence of potential and the circuit of Fi 1 be employed, the rounding of the two dimbs of the lines at the substations might sometimes be unavailing to take suflicient current from 110- lays 50 and 56 to secure the retraction of their armatures, and the release of the switches could, therefore, not be accomplished. In the employment of the struc ture of Fig. 2 the simultaneous rounding of the two limbs of their line at t e substations will Without fail, unbalance the magnetic effect of windin s 70 and 71 upon the core of rela 67 so t at armatures and 69 of said re ay will be attracted and the oil'- cuit through relays 50 and 56 entirely opened.

The employment of more than one class of selector switches, of the character herein described, is well known, and it is not my intention to limit myself to the employment of i a single selector employed for each completed connection, or to the precise structure herein shown and described, but what l claim and desire to secure by Letters Patent is:

'1. An automatic telephone exchange system including a calling subscribers line and acalled subscribers line, a connector adapted to be operated responsive to currents controlled at the callinsubstation to connect directly with the cal ed line, talking conductors for said connector having normally open switching contacts, a central source of current, a pair of relays, an electro-ma net associated with said connector efi'ective w en connection is made with the called line to close said switchin contacts whereby a circuit of said source is closed through said relag's to energize them, mechanism at the exchange adapted to be operated responsive to the simultaneous de-energization of said relays to cause the bell of the called subscribers line to ring, mechanism responsive to the'de-energization of one only of said relays, the second remaining energized, for disconnectin said lines, and switching means at tile calling substation adapted to effect the de-energization of both said relays or the de-encrgization of the one only according to the election of the subscriber.

2. An automatic telephone exchange system including a calling subscribers line and a called subscribers line, a connector adapted to be operated responsive to currents controlled at the calling substation to connect directly with the called line, talking conductors for said connector having normally open switching contacts, a central source of current, a pair of relays, back contacts for said relays closed when said relays are deenergized, a front contact for one of said rclays adapted to be closed when, said relay is energized, an electro-mugnet adapted to be energized responsive to the closing of the back contacts of both said relays to include ringing current in circuit with the called line, a second clectro-magnet ada ted to be controlled responsive to the closing of the back contact of one relay and the front contact of the other, for disconnecting aid lines, and switching means at the calling substation controlled by the subscriber for energizing and tie-energizing said relays according to the election of the subscriber. 3. A connector for automatic exchanges including a pair of talking conductors, a condenser connected in each said conductor, a central source of current connected to one of said conductors on opposite sides of its condenser, a air of relay magnets, one connected in can such connection, connections from the opposite pole of said source to the other conductor, one on each side of its condenser, a relay magnet connected in each said connection, a control circuit jointly controlled by the two magnets connected to the opposite conductors at one side of their fltl till

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connected in bridge ofsaid strandson each side of said condensers with said source in-' terposed in series between them, a source of rin ing current, a ringing relay for contro ing the application of said ringing source to the called line, a control circuit for said ringing relay including contacts of one of said pairs of relays, a release magnet for said switch, and a control circuit for said magnet including contacts of the other pair of relays. 5. A. telephone system comprising a calling line and a called line, means, including an automatic switch and a two-strand linkcircuit, for uniting said lines into a conversat-ional circuit, condensers in said strands, a source of current, a pair of relays connected in bridge of said strands on each side of said condensers with said source interposed in series between them, a source ot ringing current a ringing relay for controlling the application of said ringing source to the called line, a control circuit for said ringing relay including contacts of one of said pairs of relays, a release magnet for said switch, and control circuitsfor said magnet including contacts of both said pairs of relays.

(3, A tele hone system comprising acalling line am :1 called line, means, including an automatic switch and a two-strand link circuit, for uniting said lines into acouversational circuit, condensers in said strands, a source of current, a pair of'relays connected in bridge of said strands on each side of said condensers with said source interposed in series between them, means for applying ringing current to the called line including a circuit extending through contacts of one of said pairs of relays, and a release circuit for the switch including contacts of the other pair of relays.

7. A tele hone system comprising a calling line an a called line, means, including an automatic switch and a two-strand linkcircuit, for uniting said lines into a conversational circuit, condensers in said strands, a source of current, a pair of relay's connected in bridge of said strands on each side of said condensers with said source interposed in seriesbe'tween them,

means for applying ringing current to the called line including a circuit extending through contactsof one of said pairs of relays, and alternative release circuits for. the 4 switch including contacs oi both pairs of relays. v i Y a 8. A tele hone system'comprising a calling line and a called line, means, including an automatic switch and a .two strand linkcircuit, for uniting said lines into a conversational circuit, condensers in said strands, a source of current, a'pair ot relays connected in bridge of said strands on each side of said condensers and incircuit with said source, a source of ringing current, a ringing relay for controllin Y the aplication of said ringing source to t is called ine, a control circuit for said ringingrelajy including contacts of one of said pairs relays, arelease magnet for said switch, and a control circuit for said magnet including contacts of the other pair of relays.

9. A telephone system comprising a calling line and a called line, means, including an automatic switch and a, two-strand linkcir'cuit, for uniting said lines into a conversational circuit, condensers in said strands, asource of current, a pair of relays connected in bridge of said strands on each side of said condensers and in circuit with said'source, a source of ringing current, a ringin relay ,for controlling the ap liention 0 said rin ing source to the called a control circuit for said ringing relay including contacts of one of said pairs of relays, a releasemagnet for said switch, and control circuits for said magnet including contacts of both snidpairs'of relays.

10. A telephone system comprising a calling line and a called line, means, including an automatic switch and a two-strand linkcircuit, for uniting said lines into a conversational circuit, condensers in said strands, a source of current, a pair of relays, connected in bridge of said strands on each side of said condensers and in' circuitwith saidline,

l lil re eye, and a release circuit for the switch including contacts of the other pair of rei1. A telephone system comprising a calling line and a called line, means, including an automatic switch anda two-strand linkcircuit, for uniting said lines into a conversational circuit, condensers in. said strands, a source of current, a pair of relays connected in bridge of said strands on each side of said condensers and in circuit with said source, means for applying ringing current to the called line including a circuit extending through contacts of one of said pairs of relays, and alternative release circuits for the switch including contacts of both pairs of relays.

12: A telephone system comprising calling and called lines, a two-strand link-circut for use in connecting saidlines into a conversational circuit, condensers in said strands, a pair of relays connected in bridge of said strands on each side of said condensers, a source of ringing current, control circuits including contacts of each pair of relays, and a differential relay controlled over one of said lines and operative to disconnect certain of said relays.

13. A telephone system comprisin calling and called lines, a twostrand lin -circuit and automatic switch mechanism for use in connecting said lines into a conversational circuit, condensers in said strands, a pair of relays connected in bridge of said strands on each side of said condensers, a source of ringing current, a circuit for controlling the ap lication of said source to the called line inc uding contacts of one pair of said relays, a release circuit for controlling the release of said switch mechanism, including contacts of a pair of said relays, and a differential relay controlled over one of said lines and operative to disconnect certain of said relays.

14. A telephone system comprising calling and called lines, a two-strand link-circuit and automatic switches for connecting the ends of said circuit with said lines to complete a conversational circuit between them, condensers in the strands of said linkcircuit, a pair of relays connected in bridge of said strands on each side of said condensers, release magnets for said switches, a release circuit including said release magnets and contacts of a pair of said relays, and a switch control circuit including contacts of the other pair of said relays.

15. A telephone system comprising calling and called lines, a two-strand link-circuit and automatic switches for connecting the ends of said circuit with said lines to complete a conversational circuit between them, condensers in the strands of said linkcircuit, a pair of relays connected in bridge of said strands on each side of said condensers, release magnets for said switches, a release circuit including said release magnets and contacts of a pair of said relays, and a release circuit for the release magnet of one of said switches including contacts of theother pair of said relays.

16. A telephone system including subscribers telephone lines divided into groups, automatic connector switches divided into corresponding groups and provided with release magnets, trunking means for extending concurrent connectlons from calling lines of one of said groups to a grou of said connector switches, a plurality 0 relays for each of said connector switches through which current is supplied to the substations for talking purposes, a number of said relays for each connector switch be ing adapted to remain energized while the connectors are in use to irevent the energizing of said magnets and the release of the connectors.

17. A telephone connector comprisin r a pair of voice-current conductors, an in active connection in each conductor, a bridge in front of said inductive connections, a bridge back of said inductive connections, electrically-propelled and step-by-ste -actuated connecting mechanism, electrica 1y 0 erated release mechanism, a battery included in both bridges, and four electromagnets included in said bridges, thewindings of said electro-magnets constituting the sole or only artificial resistance between the battery and the voice-current conductors.

18. In a telephone exchange system the combination of a talking circuit, inductive connections in said circuit, a bridge in front of said inductive connections, a brid e back of said inductive connections, two re ays in I each bridge, a battery included in both bridges, switching mechanism controlled by at least one of said relays, release mechanism controlled by at least one of said relays, subscribers telephones receiving talking current from said battery, and subscriberoperated means for controlling the energizing of at least one of said relays, the windings of said relays constituting the sole orv on y artificial resistance between the battery and the saidtalking circuit.

19. In a telephone exchange system, the combination of a talking circuit, an inductive connection in each side of the talking circuit, a bridge in front of said inductive connections, a bridge back of said inductive connections, a pair of relays in each bridge, suitable means for supplying talking current through the windings of said relays to the -talking circuit, subscribers telephones receiving the talking current supplied through the said relay windings, switching mechanism controlled by at least one of said relays, release mechanism controlled by at least one of said relays, and subscriber-operated means for controlling the energizing of at least one of said relays, the said relay windings constituting the sole or only artificial resistance through which talking current is supplied to the talking circuit.

, 20. A telephone connector provided with a pair of voice-current conductors, an inductive connection in each conductor, a bridge in front of said inductive connections, a bridge back of said inductive connections, a pair of relays in each bridge, suitable means for supplying current through the windings of said relays to the said voice-current conductors, switching mechanism controlled by at least one of said relays, and release mechanism controlled by at least one of said relays, the windings of said relays constituting the sole or only artificial resistance lllll four relay coils constituting t through which current is supplied to the said voice-current conductors.

21. In a telephone exchange system, the combination of a calling telephone line, a' called telephone line, a selector intermediate thetwo lines, a connector intermediate the selector and the called line, subscribers telephones, subscriber-operated means for controlling the selector and connector, and means for supplying talking current through the connector to the calling and called telephone lines, said connector grovided with e sole or only artificial resistance through which talking current is supplied to the telephone lines.

22. A telephone connector comprising a pair of voice-current conductors, an inductive connection in each conductor, a bridge in front of said inductive connections, a bridge back of said inductive connections, electrically-propelled and step-by-step-actuated connecting mechanism, electrically operated release mechanism, a battery included in both bridges, four electro-magnets included in said bridges, the windings of said electro-magnets constituting the sole or only artificial resistance between the battery and the voice-current conductors, and a rim er relay controlled by at least one of sai bridged rela s.

23. In a telep one exchange system, the combination of a calling telephone line, a

called telephone line, a selector intermediate the two lines, a connector intermediate the selector and the called line, subscribers telephones, subscriber-operated means for controlling the selector and connector, means for supplying talking current through the connector to the calling and called telephone lines, said connector provided with four relay coils constituting the sole or only artificial resistance through which talking current is supplied to the telephone lines, and a ringer relay controlled by at least one of said bridged relays.

24. An automatic telephone connector provlded with a release circuit having two parallel and normall open branches, parallel voice-current con uctors, inductive connections in said voice-current conductors, a

relay bridge in front of said inductive connections, a relay bridge back of said inductive connections, a set of switch springs for each relay bridge, the. continuity of each said parallel branch being controlled by relay springs of both bridges.

25. A telephone connector provided with a release circuit having normally 0 en parallel branches, a pair of relays, anotlier pair of relays, a set of switch springs for each pair of relays, the continuity of each said parallel branch being controlled by springs ofboth pairs of relays.

26. An automatic telephone connector provided with a release circuit having two parallel and normally open branches, parallel voice-current conductors, inductive connections in said voice-current conductors,

a relay bridge in front of said inductive connections, a relay bridge back of said induc-- tive connections, a set of switch springs for each relay bridge, the continuity 0 parallel branch being controlled, by relay springs of both bridges, and means for furnishing talking current through the relay windings. a

27. A telephone connector provided with arelease circuit having normally open parallel branches, 2. pair of relays, another pair of relays, a set of switch springs for each pair of relays, the continuity of each said parallel branch being controlled by springs of both pairs of relays, and means for furnishing talking current through the relay AIZFRED H. DYSON.

each said non-inductively re- 

